Whenever you try to erase one digit from the passcode input on phone when you input a wrong digit it doesn’t delete it from the end. I think it erases from the front.
E.g. passcode ‘1234’ and you misinput ‘124’. Then use X to erase a digit, but it doesn’t erase the 4. I think it erases the 1 in front, as I tested ‘112’, erasing one digit, then ‘34’. This allows me into the app. I’m on Android, if that matters.
TLDR the X on mobile passcode erases the digit in front, not the back.